I personally don't think that having a ton of revolving credit is a good thing, but according to some Googling I did, it doesn't actually adversely affect your credit score. Still, I would rather shut down a card I never use and take a small hit on my credit score because I'd just feel more comfortable not having that line of credit out there.
That being said, if you pay your bills on time and don't let balances stay on your credit card for more than a month, your credit will be good enough to get you pretty much whatever you want.
No, having lots of revolving credit helps your score, and you're more likely to get approved for more things at higher limits. It's counter-intuitive, but it's how it works. Don't ever cancel a card, unless there's an annual fee or you've reached a provider's limit and want to apply for more of their cards with awesome promos (Chase, for example). If you're worried about credit being "out there," just use an account aggregator like Mint and check everything once a month or so. You're never responsible for fraudulent charges, and with Mint you can catch anything before it becomes a huge hassle.
I'm a little tempted, especially with the 10% back on PSN, but $100 is barely worth it for a hard pull IMO. Heck, it's not even really $100 when you bring CAG pricing into it.